Resistor construction



3- H. L. VAN VALKENBURG ET AL 8 RESISTOR CONSTRUCTION v Filed May 20, 1929 Patented Mar. 7, 1933 UNITED STATES PATENT OFFICE HERMON I. VAN VALKENBURG, OF WAUWATOSA, AND FORREST" C. MCNICOL, OF MIL- WAUKEE, WISCONSIN, ASSIGNORS T0 SQUARE D COMPANY, OF DETROIT, MICHIGAN RESISTOR CONSTRUCTION Application filed May 20,

This invention relates to resistor constructions. y

In resistor constructions as heretofore made, it has been the usual practice to form the resistors of cast iron, but this type of resistor was not wholly satisfactory, as difliculty was experienced due to the breaking of the resistors either during shipment or else when subjected to jarring or unusual stresses in use. In addition to this, the necessary expansion and contraction resulting from alter-' nate heating and cooling, in the normal operation of the device, tends to increase the chance of breaking.

Attempts have been made to use a sheet metal resistor unit, but when this sheet metal resistor unit was formed as a folded element, difficulty was experienced in holding the element properly in place, so that on the one hand it did not sag and on the other hand it was free from excessive tension when it contracted. In addition to this, the sheet metal strips are not inherently rigid, particularly when they are heated, and, consequently, the construction had to be relatively elaborate and relatively expensive in order to be at all eflective. The construction, however, was not satisfactory in the previous forms of which we are aware, as it had one or more defects, certain of which have been outlined above. I

Where a flexible sheet metal strip is wound upon a core, it has been found that the circulation of air is materially reduced, even when the strip is wound edgewise. Although the exact reason for this result may not be precisely known at this time, it is believed that the air tends to cling to the central core and thus retard to a material extent the flow of air past the resistor. When it is considered that the resistors ordinarily employed depend for their cooling upon the flow of air, it is immediately appreciated that anything that retards this flow causes excessive heating, with rapid deterioration of the resistor.

In addition to the defects noted above, resistors, as heretofore constructed, are so made that when the insulation supporting the resistor breaks, short circuit frequently results as the insulator usually drops out of place 1929. Serial N0. 364,375.

and the resistor contacts with the metal of the frame or associated member.

Further than this, it has been found diflicult with sheet metal resistors, to provide suflicient surface insulation to conform to the requirement of the underwriters and secure safety of operation, without making the device bulky and without increasing its cost.

This invention is designed to overcomethe defects noted above, and objects of such invention are to provide a novel form of resistor construction which is so made that the resistor element may be formed of a sheet metal strip of nonoxidizing characteristic, such, for example, as nichrome, which is held in such a manner that there is no possible chance of sagging so as to cause short circuiting of the parts, and which is so constructed that there are no excessive stresses imposed upon this strip due to alternate ex pansion and contraction when it is in use, and so that there is a free and unobstructed flow of air, permitting the resistor to be used continuously, if desired, at its maximum capacity without deterioration and without excessive heating.

Further objects are to provide a resistor construction in which the insulating members supporting the flexible strip are so constructed that good surface insulation is at all times secured, and in which means are provided for securely retaining the insulators in operative position, so thateven if cracking should occur, there is no chance for the insulation, or any portion thereof, to fall out of place.

The invention, in its broadest aspect, is not limited to a flexible strip, as it is obvious that the construction, as will appear hereinafter, is such that other types of resistance elements may be employed and the beneficial and highly desirable results outlined immediately above may be secured. Therefore, further objects of this invention are to provide a resistor which is so constructed that it cannot get away from the frame or from the insulation, in which short circuits cannot occur although the resistor is subjected to extreme abuse, in which an interlocking frame and insulator construction is obtained, and

in which the parts have a slight amount of freedom, so that excessive stresses due to changes in length are not produced.

Further objects of this invention are to 6 provide a resistor construction in which there is no direct radiation of heat to the supporting panel, which the insulators may be made up in sections, so that there is less chance of warping and cracking than here- 10 tofore, and in which the end terminals are so constructed that they interlock with the insulators and are supported by the insulators themselves, thus relieving the resistance unit of stresses although permitting the positioning of the terminals at any point along the resistance element.

Although the invention is not limited to the use of porcelain as an insulating element, nevertheless, the invention permits the use of porcelain as an insulating element in a resistor construction in such a manner that the porcelain or other heat resisting, high value dielectric material may be employed with.

safety although such material may be brit tle, as it is not subjected to tension but only to compression, and as it may be used in relatively short lengths to avoid warping and cracking.

Further objects are to provide a resistor construction in which a frame is employed and removably receives the insulating members which in turn carry the resistance element, in which any number of lengths of insulating members and resistance elements may be used, and in which means are provided for holding the frame parts together and for retaining the insulating members in place.

Further objects are to provide a resistor construction which is simple,.which is easy to produce and assemble, and which may be cheaply produced.

Before entering the detailed description of this invention, it is to be distinctly understood that the invention in its broadest aspects is not limited to an air cooled resistor, nor to a resistor formed of metal ribbon, nor to a resistor in which porcelain is used for the insulating members.

An embodiment of the invention, which has been found highly practical and effective in actual use, is shown in the accompanying drawing, in which:

Figure 1 is a view of the resistor, parts 55 being broken away and parts being in section.

Figure 2 is a sectional view on the line 2-2 of Figure 1.

Figure 3 is a sectional view on the line 60 3-3 of Figure 1.

Referring to the drawing, it will be seen that the resistor comprises a panel or frame which is composed of a pair of spaced metal channel members 1, which are held in spaced 65 relation in any suitable manner, as by means of the end brackets or bars 2. The channel members 1 are provided with inturned marginal flanges 3, and the end members or brackets 2 are provided with inturned ends 4, which fit within the channel members, and which may be secured thereto by means of screws 5, or any other suitable fastening members.

A plurality of insulating members 6 are carried by each channel member, and preferably these insulating members are formed of porcelain or other material which has a high heat resisting characteristic and a high dielectric strength. The insulating members are provided with longitudinally extending grooves 7, into which the inturned marginal flanges 3 of the channel members 1 loosely lit, to thus interlock the insulating members with the channel members. It is to be appreciated that other modes of interlocking may be followed if desired, although the form shown has been found in actual service to give excellent results. The interlocking permits the simple and easy positioning of successive insulating members to any number desired, and also has the very important effect orresult of holding the insulating members in position although through excessive abuse, as by dropping, striking, or other jars, the members may have become cracked. In other words, although the insulating members may become broken under unusual conditions, nevertheless they are securely retained in place and function as insulators even in their broken condition.

It is to be noted that the inturned ends 4 of the end members 2 serve as stops for the insulating members 6. Obviously the channel side bars 1 may be made of any desired length and any number of insulating sections may be used. Further, the construction is such that it is not necessary to form the insulating members in one continuous length. This would be difiicult if porcelain or similar insulating members were employed, as they tend to warp during baking. However, when they are 'made in relatively short sections as indicated in the drawing, it is an easy matter to secure them in an unwarped condition.

Each of the insulating members s provided with a series of sockets 8, which have relatively narrower side sockets or extensions 9. In other words, the sockets-have relatively deeper portions for the reception of the resistance element and have relatively shallower portions for the reception of the extensions of terminal members hereinafter described. This construction provides sockets any one of which is adapted to receive either one loop of the resistance element alone, or else a loop of the resistance element and a portion of the extensions 13 and 16 of the terminal members hereinafter described. These sockets are formed at regular intervals, and are so positioned that when successuitable elements.

sive insulating members abut as shown in Figure 1, the sockets adjacent the ends of successive insulating members are correctly spaced.

In the form of the invention shown, a tapelike resistance unit 10 is employed. This resistance unit is provided with reverse folds or loops, that is to say, it is folded back and forth in a zigzag manner. The looped ends are rece ved within the sockets 8, and are thus loosely though securely retained in place. No stresses are imposed upon these members in assembling, and they are free to slightly adjust themselves during heating and cooling. Further than this, the looped or folded ends are not held rigidly, nor are they passed over pins or other members. Instead they are seated within opposed sockets, and are thus securely positioned against accidental displacement even dur'ng severe use.

The resistance element may be of any nonoxidizing, heat resisting, resistance material, such, for example, as nichrome.

End terminals 11 are attached to the resistance element at any point along its length. These end terminals may consist of a pair of spaced clamping elements, between which any desired sect on of the resistance unit or element may be clamped. The main body of the end terminals 11 is preferably provided with a plate or clamping member 12, which stands at right angles to the body portion 11. This plate is provided with an extension 13, which is reduced and which normally 'fits within one of the sockets, ts ends or outer corners fitting within the portion 9 of the socket, as shown most clearly in Figure 3. The other clamping member 0? the end terminal has a plate-like portion 14 opposed to the plate 12 and drawn towards the plate 12 by means of screws 15, or any other The plate 14 is provided with an extension 16 corresponding to the extension 13, but projecting in the .opposite direction. The extension 16 fits within the portion 9 of one of the sockets. It is to be noted that the terminal members 11 are provided with a laterally projecting portion, which in turn is provided with an angularly bent conductor-receiving portion. This construction permits the assembling of successive units in close proximity and yet provides sufficient strength and cross sectional area for the terminal members.

It is clear that the body portions 11 of the terminal members afford a ready means for attachment to the conductors leading to the resistor. Also it is clear that the end ternrnals may be attached at any point along the length of the resistance element either before or after the device is assembled. In attaching the end terminal to the resistance element the extensions 13 and 16 are slipped into the appropriate sockets, and thereafter the screws 15 are inserted and tightened, to

thus clamp a portion of the resistance element between the plates 12 and 14 of the terminal member, and to hold the terminal member locked to the insulating members 6. The terminal members are thus directly locked to the insulating members, and are directly supported from the insulating members. The weight and stresses imposed by the terminal members are not borne by the resistance element, but are borne by the insulating members. Thus there is no chance of twisting, breaking, or distorting the resistance element by the terminal members.

It is to be noted further that although porcelain is brittle, nevertheless it may be safely used in this construction, for if the porcelain should be cracked from any cause, it cannot fall free of the frame, but is retained by the interlocking of the frame and the insulators.

Further, there is a high surface insulation secured by this construction, for there is a relatively long path along the surface from the resistance element to the frame.

In addition to this, the assembling of the apparatus is very simple. All that is necessary is to fit the looped portions of the resistance element into the appropriate sockets, and thereafter slip the insulating members into place in interlocking engagement with the channel members.

It will be seen, therefore, that a very simple, serviceable and rugged type of resistor construction has been provided by this invention.

Although the invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

We claim:

1. A resistor construction comprising a frame having opposed channel members, means for holding said channel members in spaced relation, insulators carried by said channel members, means for retaining said insulators within said channel members, said insulators having a series of sockets formed therein, a reversely folded resistance unit having its folded portions seated within said sockets, said sockets having side extensions, and a terminal member seated in said side extensions and connected to said resistance unit.

2. A resistor construction comprising a pair of spaced insulators having sockets therein, a resistance element looped back and forth between said insulating members, the insulators being located wholly upon opposite sides of said resistance element and a terminal clip adapted to be secured to said resistance element and having projecting portions adapted toseat in any of said sockets.

' bers '3. A resistor construction comprising a pair of opposed, spaced insulating members, each having spaced sockets therein, a re sistance element having reversely formed, looped portions fitted within said sockets, and a terminal member having a pair 0 clamping portions adapted to clamp said resistance element at any point along its length and having oppositely projecting extensions adapted to seat in any of the said sockets, whereby said terminal member is supported by said insulating members.

4. A resistor construction comprising a frame having opposed channel-shaped memprovided with inturned marginal flanges, insulating members carried within said channel members and having grooves formed therein into which said flanges project, to thereby inter-lock with said insulating members, said insulators having outer portions overhanging the flanges of said channel members, and a resistance element extending between said insulating members,

whereby the surface insulation distance is increased between the resistance element and the frame by the overhanging portion of said insulating members.

5. A resistor construction comprising a frame having opposed channel-shaped members provided with inturned marginal flanges, insulating members carried within said channel members and having grooves formedtherei'n into which said flanges project, to thereby inter-lock with said insulating members, a resistance element extending between said insulating members, and a clamp forming a terminal member adapted to clamp said resistance element at any "point along its length, said clamp having projecting portions adapted to engage and be supported by said insulating members at points spaced from the point of contact with said resistance member. I

6. A resistor construction comprising a pair of opposed frame members, insulating members carried by said frame members and having sockets formed therein, a looped resistance element carried between said insulating members and having folded portions located within said sockets, and a terminal member'adapted to engage sald resistance element and having extensions seated within certain of said sockets, said terminal member being formed of a pair of clamping members adapted to engage the resistance element and having means for drawing the clamping members towards each other, said insulating members being located wholly upon opposite sides of said resistance element.

7. A resistor construction comprising an elongated frame having opposed longitudinally extending portions,

insulating members carried by said portions, a reversely folded resistance element carried between said insulating members, and a terminal member supported by said insulating members and secured to said resistance element, said terminal member having a laterally projecting portion provided with an angularly f bent conductor-receiving portion lying in a plane paralleling the plane of the frame.

In testimony whereof, the signatures of the inventors are aifixed hereto.

HERMON .L. VAN VALKENBURG. FORREST C. MoNICOL. 

